[mrtg] Re: bandwidth utilisation

[Alex van den Bogaerdt]

Rich Adamson wrote:

[correct quoting order restored]

> > Both MRTG and RRDtool have no way of knowing that a counter has
> > incremented by more than 2^32. Switching to RRDtool doesn't help here.

> That may not be totally correct. The RRDtool can poll remote devices
> at a much faster rate. If the tool is polling faster than what the
> counters are rolling over, it could be beneficial. 

While your statement about RRDtools ability to poll more frequent
is technically correct, so is my statement about 2^32.

Buying faster boxes with more memory, cpu, bus and so on than you and
I can afford will also allow MRTG to poll devices more frequently.

A big problem with polling more often is that, at least this is my
opinion, the error introduced in the measurement increases.  If you
have a timing error of 1 second every 300 seconds vs. the same 1-second
error every 60 seconds then this is already a huge increase.  I also
believe that a busy computer will increase the 1-second error to, for
instance, a 2-second error.  In the end you'll end up with a 1:30 ratio
in stead of a 1:300 ratio.  At 100Mbps a 2-second error over a 60-second
interval translates into 6200 Mb per 60 seconds is over 103.33 Mbps for
one interval and less than 96.67 Mbps the next interval.  At the usual
error factor it would be 100.33 vs. 99.67 ...  Note that these numbers
are fictional but reasonable.

cheers,
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